Answer the following questions. Your answers should be clear and short.What is semantic unity of idioms?
（1）AN IDIOM MAY CONSIST OF MORE THAN ONE WORD, EACH HAS ITS MEANING, AND PART OF SPEECH.
（2）HAS A SINGLE MEANING.
（3）FUNCTIONS AS ONE WORD-EQUIVALENT.
（4）IN MANY CASES, ILLOGICAL RELATIONSHIP BETWEEN THE LITERAL MEANING OF THE CONSTITUENT WORD AND THE MEANING OF THE WHOLE IDIOM.
